The African National Congress's (ANC's) parliamentary caucus has called a special meeting ahead of a National Assembly vote on Tuesday afternoon on whether the legislature should institute an inquiry into Public Protector Busisiwe Mkhwebane's fitness to hold office.

In recent days, divisions among ANC MPs have spilt into the open over whether the party should support such an inquiry. These led to reports of an unusual meeting between chief whip Pemmy Majodina and the party's top six on Monday.

Caucus spokesperson Sinetemba Jakavula confirmed Tuesday's lunch meeting: "There are internal matters to be discussed." But Jakavula didn't elaborate.

On Tuesday, she denied that Majodina had met the ANC leadership. Party spokesperson Pule Mabe said he wasn't aware that a meeting had taken place but said he would check whether it did. 

When approached for comment, Majodina said she wasn't prepared to talk about the matter.

The last caucus meeting on Thursday, the scheduled time for the party's weekly caucuses, was longer than usual due to disagreements between MPs over the matter.

Over the weekend, Majodina issued a statement saying the caucus supported the process to hold an inquiry.

ANC secretary-general Ace Magashule earlier said no "principled" ANC MP would vote in favour of the inquiry, which needs a simple 50 percent plus one majority in the National Assembly. 

The ANC holds 249 out of the 400 seats so a vote in favour of an inquiry would need support from at least part of the governing party's caucus. 

ANC MPs Mervyn Dirks and Supra Mahumapelo later released letters in which they openly disagreed with Majodina's weekend statement. 

Dirks wrote that the caucus did not agree that Mkhwebane's impeachment should go ahead and that there were two views.

He also claimed that there wasn't time during the meeting for everyone to air their views. 

In her statement, Majodina said it was premature to conclude whether the voting would be for the retention or removal of the Public Protector.

A decision to impeach Mkhwebane would require support from two-thirds or 267 MPs. 

Analysts said the vote would be a big test for the ANC because a report by an independent panel, which was made public this month, recommended that an inquiry should be held because there was strong evidence in favour of impeachment.